Molded cooling fan

ABSTRACT

A cooling fan assembly ( 10 ) includes a hubless polymer fan body molded around the perimetrical flange ( 20 ) of a metallic mounting hub ( 12 ). The fan body includes a circumferential ring ( 18 ) interlocked with the flange ( 20 ) and a plurality of fan blades ( 16 ) projecting outwardly from the ring ( 18 ). The fan body ( 14 ) is formed in an injection mold with molten polymer material being introduced into the mold at hot runner locations ( 25 ) disposed between the circumferential ring ( 18 ) and the root diameter ( 17 ) of the fan blades ( 16 ). At one face of the hubless fan ( 14 ), the circumferential ring ( 18 ) includes a plurality of uniformly spaced raised bosses ( 30 ). Each boss ( 30 ) defines a bore ( 31 ) configured to receive a balancing weight therein, preferably in the form of a balancing screw ( 35 ) threaded into the bore. The bosses ( 30 ) are interconnected by a stiffening ring ( 33 ) having a height substantially equal to the height (h) of the bosses ( 30 ). The stiffening ring ( 33 ) is modified between a plurality of pairs of bosses ( 30 ) to define a recessed flat ( 38 ). On the opposite face of the hubless fan ( 14 ), the circumferential ring ( 18 ) includes a plurality of raised tabs ( 40 ), arranged and configured to mate within a corresponding recessed flat ( 38 ). The corresponding recessed flats ( 38 ) and raised tabs ( 40 ) nest between stacked fan assemblies ( 10 ) to enhance the stability and increase the number and height of stacked sets of assemblies.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to cooling fans such as fans usedin connection with an automotive or industrial cooling system. Morespecifically, the invention pertains to fans with integral blades formedin a molding process, such as an injection molding procedure.

[0002] Most automotive and industrial power components require some formof auxiliary cooling system. In a typical automotive application, thiscooling system includes a radiator and a cooling fan that directs airacross the radiator. In these applications, the fan is mounted to arotating flange of a fan drive that is separate from the power plantoutput.

[0003] In the early design of such cooling fans, metal blades weremounted to a metal hub, which hub was then attached to the fan drive. Inrecent years, however, high-strength polymer materials have been used toform various components of the fan. The polymer fan design was found tobe capable of withstanding the normal forces and stresses endured by acooling fan in even the heaviest duty automotive or industrialapplication. Moreover, the use of polymer materials provided asignificant reduction in weight of the cooling fan. Moreover, andperhaps most significantly, the use of polymers generated significantbenefits in the manufacture of the fan, since materials of this typereadily lend themselves to a variety of molding processes.

[0004] The one-piece molded fan has eliminated the welds and rivetscommonly associated with prior metal fans. In addition, the moldingprocess facilitated the generation of smooth rounded contours, whichultimately reduced internal stresses within the fan structure.

[0005] In one type of molded fan design, the entire fan and hub areformed in a single piece. An example of this form of a one-piece moldedfan is shown in U.S. Pat. No. 4,671,739 to Read et al. Fans of this typewere found to be better suited for smaller duty applications, such asfor use in the cooling system of passenger automobiles. For larger,higher stress applications, a hubless molded fan design was found to bemore appropriate. One such design is depicted in U.S. Pat. No. 5,593,283to Scott. In this design, a polymer hubless fan is integrally formedaround a metallic mounting hub. This mounting hub can be supportedwithin the molding apparatus, such as a typical injection moldingmachine. The polymer material is then injected into a mold surroundingthe hub to form an interlocking ring around the metal hub.

[0006] In many automotive and industrial applications the molded fanincludes a polymer, such as polypropylene, nylon or other resincompositions. In addition, many industrial fans include reinforcingmaterial such as glass fibers or nylon strands. The reinforcing materialcan be oriented within the structure of the molded fan blade to provideadditional strength and stiffness where needed based upon stressanalysis of the working fan.

[0007] The hubless fan design has evolved since its inception. While themetal mounting hub provides a certain degree of strength to the overallfan, the molded fan can include an enlarged polymer ring formed aroundthe mounting hub. This ring helps provides strength and bending orflexure stiffness to the root of each of the fan blades.

[0008] While the hubless polymer fan represents an improvement overprior metal and one-piece polymer fan constructions, improvements arestill needed. For instance, cost and material considerations areimplicated by current molded fan designs involving significant materialwaste. Cost considerations are also involved in the storing and shippingof an inventory of fans. There remains a need for a molded fan assemblythat reduces the overall costs associated with manufacturing andshipping the final fan product.

SUMMARY OF THE INVENTION

[0009] In order to address the needs unmet by prior fan designs, thepresent invention contemplates a fan assembly comprising a substantiallyrigid hub configured for mating with a fan drive and defining aperimetrical flange. A hubless fan includes a circumferential ringmolded about the perimetrical flange of the rigid hub, and a pluralityof outwardly projecting fan blades integrally formed with the ring.

[0010] In one embodiment of the invention, the hubless fan furtherincludes a plurality of hot runners for introduction of molten materialinto the hubless fan that are radially disposed between thecircumferential ring and the root diameter of the fan blades. With thisfeature, molten polymer material is distributed more uniformlythroughout the molded hubless fan. Moreover, less material is wasted inthe form of a cold sprue that must be trimmed from the completed fanassembly. In a further aspect, each of the hot runners is raisedrelative to the circumferential ring, which allows the hot runners tohave a larger diameter to accept greater flow of molten material intothe hubless fan mold.

[0011] In a further embodiment of the invention, the circumferentialring of the hubless fan defines a plurality of bores dispersed about thecircumference of the ring. Each of the bores is configured for receivinga balance weight therein. In the most preferred embodiment, the balanceweight is in the form of a screw having a known weight and includingself-tapping threads for screwing into a specific one of the bores. Thering defines a predetermined number of the bores radially aligned with acorresponding one of the fan blades, namely four such bores in the mostpreferred embodiment. Standard rotating body balancing techniques can beused to determine the magnitude of weight and the boss location for theaddition of the balancing screw.

[0012] In another aspect of this inventive feature, the circumferentialring includes a plurality of raised bosses in which each of the bossesincludes a corresponding one of the plurality of bores. The bosses havea height from the circumferential ring, and the bores have a depth nogreater than that height to avoid compromising the body of thecircumferential ring supporting the fan blades. A stiffening ring isformed between and interconnecting adjacent ones of the plurality ofraised bosses that has a height substantially equal to the raised heightof the bosses.

[0013] The present invention also provides a feature to enhance thestackability of the fan assemblies. In another aspect of the invention,the stiffening ring defines at least two recessed flats between acorresponding adjacent pair of raised bosses. The stiffening ring has areduced height at each of the recessed flats that is less than theheight of the stiffening ring of bosses. On the opposite face of thehubless fan, the circumferential ring further includes at least tworaised tabs projecting therefrom. Each of the tabs is sized and arrangedto reside within a corresponding one of the recessed flats. Thus, whentwo or more of the hubless fans are stacked, the raised tabs of one ofthe fans nests within corresponding ones of the recessed flats of anadjacent one of the hubless fans.

[0014] In a preferred embodiment, the number of raised tabs and recessedflats equals the number of fan blades. The tabs and flats can besituated in radial alignment with the gap between adjacent fan blades.

[0015] It is one object of the present invention to provide a fanassembly utilizing a hubless fan that minimizes the amount of materialrequired to form the fan in a molding process. Reducing the amount ofmaterial waste is also accomplished by features of the invention thateliminate the need to trim blade material for balancing the fanassembly.

[0016] Another object of the invention is directed to improving thestackability of molded fan assemblies. An added object resides infeatures that enhance the stability of a stack of such fan assemblies.

Other objects and particular benefits of the invention will becomeapparent to a person of skill in this art upon consideration of thefollowing written description and accompanying figures. DESCRIPTION OFTHE FIGURES

[0017]FIG. 1 is a top elevational view of a fan assembly according toone embodiment of the present invention.

[0018]FIG. 2 is a partial bottom elevational view of the opposite sideof the fan assembly shown in FIG. 1.

[0019]FIG. 3 is a side cross-sectional view of the fan assembly shown inFIG. 1 taken along line 3-3 as viewed in the direction of the arrows.

[0020]FIG. 4 is a partial cross-sectional view of the fan assemblydepicted in FIG. 2, taken along line 4-4 as viewed in the direction ofthe arrows.

[0021]FIG. 5 is a side, partial cross-sectional view of a pair of fanassemblies such as the assemblies of FIG. 1 and 2, shown in a stackedconfiguration.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] For the purposes of promoting an understanding of the principlesof the invention, reference will now be made to the embodimentsillustrated in the drawings and specific language will be used todescribe the same. It will nevertheless be understood that no limitationof the scope of the invention is thereby intended. The inventionincludes any alterations and further modifications in the illustrateddevices and described methods and further applications of the principlesof the invention which would normally occur to one skilled in the art towhich the invention relates.

[0023] Referring to FIG. 1, a fan assembly 10 is depicted which includesa mounting hub 12 and a separate hubless fan 14. In the preferredembodiment, the mounting hub 12 is formed of metal and is mostpreferably configured as a stamped circular plate. The configuration ofthe mounting hub 12 will vary depending upon the fan drive to which thefan assembly 10 is connected. In the illustrated embodiment, themounting hub 12 includes a mounting hole array 23 that includes a numberof openings for receiving mounting bolts of the fan drive. In someinstances, the mounting hub 12 can simply constitute a flat annulardisc. In other instances, such as that depicted in the sidecross-sectional view of FIG. 3, the mounting hub 12 is dish-shaped. Itis understood, of course, that the configuration of the mounting hub 12is not essential to the present invention, and instead can be dictatedby the application of the particular fan assembly 10.

[0024] The hubless fan 14 in the preferred embodiment is a moldedpolymer fan that includes integrally molded blades 16. In theillustrated embodiment the hubless fan 14 includes nine (9) blades andhas a diameter of 28 inches (71 cm.). The number of blades and theirconfiguration (e.g., thickness, chord dimensions and curvature) can bedictated by the specific application for the fan assembly 10. The fanassembly 10 of this configuration can be used in a variety ofapplications, such as for a medium-duty truck cooling system fan.

[0025] Each of the blades 16 is integrally formed with a uniformlymolded polymer ring 18. The ring 18 presents a region of increasedthickness relative to the thickness of each of the blades 16. Inaddition, the ring 18 is molded around the perimeter flange 20 (see FIG.3) of the mounting hub 12. The molded ring 18 and perimeter flange 20are most preferably of an interlocking design. In other words, theflange 20 can include a plurality of openings 21 defined therethrough.When the hubless fan 14 is molded about the mounting hub 12, the polymermaterial flows through each of the openings 21 and sets in place to formthe molded ring 18. This interlocking feature prevents the hubless fan14 from rotating relative to the mounting hub 12.

[0026] Since the hubless fan 14 is a molded polymer material, the fanincludes a number of locations at which the molten polymer material isintroduced. More specifically, the fan 14 includes a plurality of hotrunners 25 dispersed circumferentially around the molded ring 18 of thefan. Each of the hot runners 25 is arranged between adjacent blades 16so that the weld line or knit line is located generally in the center ofeach blade, as is known in the art. However, in one unique aspect of theinvention, the hot runners 25 are situated between the molded ring 18and the root diameter 17 of each of the fan blades 16.

[0027] In a further departure from prior fan molding processes, the hotrunners 25 in accordance with the present invention are raised slightlyfrom the surface of the molded ring 18 of the hubless fan 14. Increasingthe height of the hot runners allows these runners to be larger than inprior systems. This increased runner size, coupled with locating therunners outboard of the molded ring 18, allow the present molded fan 14to be formed more efficiently with less material waste.

[0028] In prior molding processes, a cold sprue and runner system isutilized in which the sprue and runners are situated at the interior ofthe hubless fan body. A molding arrangement of this type is shown inU.S. Pat. No. 4,957,414 to Willingham. In practice, the cold sprues orslugs must be removed after the fan has been assembled. With the presentinvention, the location of the hot runners does not require the samesprue removal step. This approach of the present invention reduces theamount of material that must be removed, and therefore reduces theamount of waste associated with the manufacture of each fan assembly 10.Moreover, locating the hot runners outboard of the molded ring 18 allowsthe molten polymer material to flow more uniformly into the fan blademold regions and into the ring mold sections. This increased flowuniformity results in a hubless fan blade with significantly fewermaterial voids that might compromise the integrity and strength of thefan assembly 10.

[0029] A further feature of the invention pertains to balancing the fanassembly. It is of course well known that any rotating component must bebalanced to avoid excessive vibration and torque. In a typical prior artmolded fan, this balancing is accomplished by removing material from thetips of one or more fan blades. This process is cumbersome and wastefulof material, and in some instances disruptive of the overall performanceof the fan assembly. Moreover, removing blade material leaves littleroom for error-the excised material cannot be restored if the fanassembly is not balanced. In extreme cases, an entire fan assembly maybe scrapped if the balancing process leads to the removal of too muchblade material.

[0030] In accordance with the present invention, the molded hubless fan14 is provided with a ring of balance bosses 30 formed at one side ofthe molded ring 18 of the fan 14, as seen best in FIG. 2. These balancebosses 30 are preferably uniformly dispersed around the inner perimeterof the hubless fan 14 adjacent the root of each of the blades 16, andmost preferably are formed as part of the molded ring 18. In thepreferred embodiment, four (4) such balance bosses 30 are aligned witheach blade 16.

[0031] Each of the balanced bosses 30 defines an internal bore 31 thatis configured to receive a balance weight, such as a rivet or screwtherein. In a specific embodiment, as depicted in FIG. 4, the balanceweight is a balance screw 35 that is threaded into the bore 31 of aparticular balance boss 30. Each balance screw 35 can have a knownweight, and a selection of differently weighted balance screws 35 can beprovided. The circumferential location and necessary weight forbalancing the fan assembly 10 can be established using traditionalrotating balancing techniques.

[0032] In order to preserve the integrity of the molded ring 18 of thehubless fan 14, the balance screws 35 are sized to be entirely disposedwithin the balance boss 30. In other words, each of the bosses 30projects upward from the molded ring 18 by a predetermined height h(FIG. 4). In one specific embodiment, that height h is about 0.375inches (0.95 cm.). For this specific embodiment, the balance screws havea threaded length of less than the boss height. The balance screw 35 canhave a variety of configurations. For instance, the enlarged head ofscrew 35 can be eliminated, the threads can be self-tapping oreliminated in favor of a press-fit configuration, etc.

[0033] With the added height provided by each of the balance bosses, thehubless fan 14 further includes a stiffening ring 33 extending betweeneach boss, as depicted best in FIGS. 2 and 4. Nominally, the stiffeningring 33 has a height equal to the height h of each of the balance bosses30. In the illustrated embodiment, the balance bosses are uniformlyspaced about the circumference of the molded ring. Alternatively,non-uniformly spaced bosses may be utilized, as well as varying numbersand sizes of such bosses, provided that a sufficient number of balancebosses are available to accurately balance the fan assembly 10. Forlarger fan assemblies, two or more rows of balance bosses, such asbosses 30 can be provided, with bosses in adjacent rows offset relativeto each other.

[0034] In a further aspect of the invention, the stiffening ring 33 ismodified between a few pairs of balance bosses 30 to define a recessedflat 38. More specifically, a pair of balance bosses 30 associated witheach pair of fan blades 16 includes the recessed flat 38 definedtherebetween. The recessed flat preferably has a thickness greater thanthe thickness of the stiffening ring. On the other hand, the flat 38 hasa height that is less than the height h of the balance bosses 30, asbest seen in FIG. 4.

[0035] The position of each of the recessed flats 38 corresponds to theposition of a plurality of raised tabs 40 are formed on the oppositesurface of the molded ring 18. The position of the tabs 40 is best seenin FIGS. 1 and 3. The raised tabs 40 are dimensioned to fit in contactwith the recessed flats 38 between adjacent balance bosses 30. In aspecific embodiment, the raised tabs 40 have a height equal to the depthof the recessed flats 38 below the top surface of the balance bosses 30.In a specific embodiment, that height is about 0.25 inches (0.6 cm.).

[0036] As can be seen by a comparison of FIGS. 1 and 2, the number andlocation of the raised tabs 40 corresponds to the number and location ofrecessed flats 38. In the illustrated embodiment, nine such tabs 40 andflats 38 are provided, each being oriented in the gap between adjacentblades 16. Of course, other orientations and numbers of flats and tabscan be provided, as long as the same number and positioning of onecomponent relative to the other component is maintained.

[0037] It is known that newly manufactured fan assemblies are stackedfor storage or shipping. In the usual case, the fan blades rest uponeach other to support adjacent fan assemblies in the stack. Thisstacking arrangement is unstable and often detrimental to the fanblades. In other fan designs, the inner ring of the fans are stacked ontop of each other. In this instance, the fan blades are protected, butthe resulting stack is again unstable. Moreover, the stackable height ofthe fan assemblies is limited when stacked in this manner.

[0038] Referring to now to FIG. 5, the purpose behind the recess flats38 and raised tabs 40 can be discerned. In order to address theseaforementioned problems with prior molded fan designs, the presentinvention contemplates that each of the raised tabs 40 reside orinterlock within a corresponding flat 38 between adjacent balance bosses30. This interlocking stacked relationship is depicted at FIG. 5 inwhich a first fan assembly 10 and second fan assembly 10′ are stackedtogether. In this arrangement, it can be seen that the raised tab 40 offan assembly 10 contacts the recessed flat 38′ of fan assembly 10′. Withthis arrangement, the mounting hub 12′ and the blades 16′ can nestwithin the corresponding hub 12 and blades 16.

[0039] This nesting capacity reduces the overall height of the stack offan assemblies 10, 10′, etc. In addition, the interlocking aspect of thetabs and flats greatly increases the stability of the stack of fanassemblies, increased stability means that a higher, more stable, stackof fan assemblies can be provided for transport or storage than withprior fan assembly designs.

[0040] While the invention has been illustrated and described in detailin the drawings and foregoing description, the same is to be consideredas illustrative and not restrictive in character. It should beunderstood that only the preferred embodiments have been shown anddescribed and that all changes and modifications that come within thespirit of the invention are desired to be protected.

What is claimed is:
 1. A fan assembly (10) comprising: a substantiallyrigid hub (12) configured for mating with a fan drive and defining aperimetrical flange (20); a hubless fan (14) defining a circumferentialring (18) molded about said perimetrical flange (20) of said rigid hub(12) and a plurality of outwardly projecting fan blades (16) integrallyformed with said ring (18), said ring (18) defining a plurality of bores(31) dispersed about the circumference of said ring (18), each of saidbores (31) configured for receiving a balance weight therein.
 2. The fanassembly (10) according to claim 1 , wherein said ring (18) defines apredetermined number of said bores (31) radially aligned with acorresponding one of said plurality of fan blades (16).
 3. The fanassembly (10) according to claim 2 , wherein said predetermined numberincludes four bores (31) for said corresponding one of said fan blades(16).
 4. The fan assembly (10) according to claim 1 , wherein saidcircumferential ring (18) includes a plurality of raised bosses (30),each of said bosses (30) including a corresponding one of said pluralityof bores (31).
 5. The fan assembly (10) according to claim 4 , whereineach of said bosses (30) has a raised height and each of said bores (31)has a depth less than or equal to said raised height.
 6. The fanassembly (10) according to claim 4 , wherein said circumferential ring(18) includes a stiffening ring (33) formed between and interconnectingadjacent ones of said plurality of raised bosses (30).
 7. The fanassembly (10) according to claim 6 , wherein said plurality of bosses(30) have a raised height (h) and said stiffening ring (33) has a heightsubstantially equal to said raised height (h).
 8. The fan assembly (10)according to claim 7 , wherein said stiffening ring (33) defines atleast two recessed flats (38) between a corresponding adjacent pair ofraised bosses (30), said stiffening ring (33) having a reduced height ateach of said recessed flats (38) that is less than said height of saidstiffening ring (33).
 9. The fan assembly (10) according to claim 8 ,wherein: said hubless fan (14) has a first face and an opposite face;said circumferential ring (18) includes said plurality of raised bosses(30) on said first face of said hubless fan (14); and saidcircumferential ring (18) further includes at least two raised tabs (40)projecting therefrom on said opposite face of said hubless fan (14),each of said tabs (40) sized and arranged to reside within acorresponding one of said at least two recessed flats (38), whereby whentwo or more of said hubless fans (14) are stacked said at least tworaised tabs (40) of one of said fans nests within corresponding ones ofsaid at least two recessed flats (38) of an adjacent one of said hublessfans (14).
 10. The fan assembly (10) according to claim 8 , wherein saidstiffening ring (33) has a first thickness at each of said at least tworecessed flats (38) and a second smaller thickness apart from saidrecessed flats (38).
 11. The fan assembly (10) according to claim 1 ,further comprising a balance screw (35) serving as a balance weight,said screw (35) having a threaded stem configured for threadedengagement within one of said plurality of bores (31).
 12. The fanassembly (10) according to claim 1 , wherein said rigid hub (12) ismetallic and said hubless fan (14) is formed of a polymer material. 13.A fan assembly (10) comprising: a substantially rigid hub (12)configured for mating with a fan drive and defining a perimetricalflange (20); a hubless fan (14) having a first face and an opposite faceand defining a circumferential ring (18) molded about said perimetricalflange (20) of said rigid hub (12) and a plurality of outwardlyprojecting fan blades (16) integrally formed with said ring (18); saidcircumferential ring (18) defining at least two recesses (38) at saidfirst face spaced around the circumference of said ring (18); and saidcircumferential ring (18) further including at least two raised tabs(40) projecting from said ring (18) at said opposite face, each of saidtabs (40) sized and arranged to reside within a corresponding one ofsaid at least two recesses (38), whereby when two or more of saidhubless fans (14) are stacked, each of said raised tabs (40) of one ofsaid fans nests within corresponding recesses (38) of an adjacent one ofsaid hubless fans (14).
 14. The fan assembly (10) according to claim 13, wherein said circumferential ring (18) includes at least two pairs ofraised bosses (30) projecting therefrom at said first face, each pair ofraised bosses (30) defining one of said recesses (38) therebetween. 15.The fan assembly (10) according to claim 14 , wherein saidcircumferential ring (18) includes a stiffening wall (33) between andintegral with adjacent pairs of bosses (30).
 16. The fan assembly (10)according to claim 13 , wherein said circumferential ring (18) defines anumber of recesses (38) equal to the number of fan blades (16).
 17. Thefan assembly (10) according to claim 13 , wherein said hubless fan (14)includes a gap between adjacent ones of said plurality of fan blades(16), and said ring (18) defines one of said recesses (38) in radialalignment with each said gap.
 18. A fan assembly (10) comprising: asubstantially rigid hub (12) configured for mating with a fan drive anddefining a perimetrical flange (20); a hubless fan (14) defining acircumferential ring (18) molded about said perimetrical flange (20) ofsaid rigid hub (12) and a plurality of outwardly projecting fan blades(16) integrally formed with said ring (18), said plurality of bladesdefining a root diameter (17) radially outboard of said circumferentialring (18); said hubless fan (14) further including a plurality of hotrunners (25) for introduction of molten material into said hubless fan(14), said hot runners (25) being radially disposed between saidcircumferential ring (18) and said root diameter (17).
 19. The fanassembly (10) according to claim 18 , wherein each of said hot runners(25) is raised relative to said circumferential ring (18).
 20. The fanassembly (10) according to claim 18 , wherein said hubless fan (14)defines a gap between adjacent fan blades (16) and includes a hot runner(25) radially aligned with each said gap.